Over-Indexed Thermoplastic Polyurethane Elastomer, Method Of Making, And Articles Comprising The Elastomer

ABSTRACT

An over-indexed, optionally cross-linked thermoplastic polyurethane elastomer. Also, the method of making the elastomer, and articles, including golf balls, comprising the elastomer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an over-indexed, optionallycross-linked thermoplastic polyurethane elastomer, a method of makingthe thermoplastic polyurethane elastomer, and to articles, particularlygolf balls, having an over-indexed, optionally cross-linkedthermoplastic polyurethane elastomer cover.

2. Description of Related Art

Golf ball covers are generally divided into two types: thermoplasticcovers and thermoset covers. Thermoplastic polymer materials may bereversibly melted, and so may be used in a variety of manufacturingtechniques, such as compression molding, that take advantage of thisproperty. On the other hand, thermoset polymer materials are generallyformed by mixing two or more components to form a cured polymer materialthat cannot be re-melted or re-worked. Each type of polymer materialpresent advantages and disadvantages when used to manufacture golfballs.

Thermoplastic materials for golf ball covers can be usually includeionomer resin, highly neutralized acid polymer composition, polyamideresin, polyester resin, polyurethane resin, and mixtures thereof. Amongthese, ionomer resin and polyurethane resin are popular materials forgolf ball covers.

Ionomer resins, such as Surlyn® products (commercially available from E.I. DuPont de Nemours and Company), have conventionally been used forgolf ball covers. For example, Dunlop Rubber Company obtained the firstpatent on the use of Surlyn® for the cover of a golf ball, U.S. Pat. No.3,454,280 issued Jul. 8, 1969. Since then, there have been a number ofdisclosures on the use of ionomer resins in the cover composition of agolf ball, for example, U.S. Pat. Nos. 3,819,768, 4,323,247, 4,526,375,4,884,814 and 4,911,451.

However, ionomer resin covered golf balls suffer from the problem thatthe cover surface may be scraped off by grooves on a clubface duringrepeated shots, particularly with irons. In other words, ionomer covershave poor scuff resistance. Also, ionomer covered balls usually haveinferior spin and feel properties as compared to balata rubber orpolyurethane covered balls. The use of softer ionomer resins for thecover will improve spin and feel to some extent, but will alsocompromise the resilience of the golf balls because such balls usuallyhave a lower coefficient of restitution (COR). Furthermore, the scuffresistance of such softer ionomer covers is often still notsatisfactory.

Thermoplastic polyurethane elastomers may also be used as the covermaterial, as described in (for example) U.S. Pat. Nos. 3,395,109,4,248,432 and 4,442,282. However, the thermoplastic polyurethaneelastomers disclosed therein do not satisfy all the requirements ofmoldability, hitting feel, control, resilience, and scuff resistanceupon iron shots.

US Patent Application Publication No. 2011/0081492 (the '492publication) disclosed a method of curing polyurethane composition foruse in constructing golf balls by i) mixing isocyanate and polyolcompounds to produce a polyurethane prepolymer; ii) chemically-curingthe prepolymer by reacting it with a hydroxyl-terminated curing agent ata stoichiometric ratio of isocyanate groups to hydroxyl groups of atleast 1.20:1.00 to form a composition; iii) applying the compositionover the core and allowing it to partially-cure; and iv) moisture-curingthe composition to form a fully-cured cover layer comprising apolyurethane/urea composition. However, the '492 publication fails toteach or suggest controlling a ratio of the organic isocyanate to thelong chain polyol from 1.06:1.00 to 1.18:1.00. Also, the '492publication fails to teach or suggest to use a cross-linkedthermoplastic polyurethane having cross-links located in the hardsegments as an outer cover layer and a small thermoplastic inner corelayer.

On the other hand, thermoset polymer materials such as polyurethaneelastomers, polyamide elastomers, polyurea elastomers, diene-containingpolymer, cross-linked metallocene catalyzed polyolefin, and silicone,may also be used to manufacture golf balls. Among these materials,thermoset polyurethane elastomers are popular.

Many attempts, such as are described in U.S. Pat. Nos. 3,989,568,4,123,061, 5,334,673, and 5,885,172, have been made to use thermosetpolyurethane elastomers as a substitute for balata rubber and ionomerresins. Thermoset polyurethane elastomers are relatively inexpensive andoffer good hitting feel and good scuff resistance. Particularly,thermoset polyurethane elastomers may present improvements in the scuffresistance as compared to softened ionomer resin blends. However,thermoset materials require complex manufacturing processes to introducethe raw material and then effect a curing reaction, which causes themanufacturing process to be less efficient.

Scuff-resistant, durable materials also are important in othertechnologies. For example, articles such as livestock identity tags,shoe soles, and sports balls of many types, require a durable,scuff-resistant surface.

Accordingly, for the foregoing reasons, there is a need in the art for asystem and method that addresses the shortcomings of the prior artdiscussed above.

SUMMARY OF THE INVENTION

In one aspect, this disclosure relates to an over-indexed thermoplasticpolyurethane elastomer, and to a method for making the thermoplasticpolyurethane elastomer. The thermoplastic polyurethane elastomer has anNCO index of at least about 1.01, typically at least about 1.06, moretypically between about 1.06 and about 1.35, and further typicallybetween about 1.06 and about 1.18.

In another aspect, this disclosure relates to an over-indexedcross-linked thermoplastic polyurethane (TPU) elastomer, and to a methodfor making the TPU elastomer. The thermoplastic polyurethane elastomerhas an NCO index of at least about 1.01, typically at least about 1.06,more typically between about 1.06 and about 1.35, and further typicallybetween about 1.06 and about 1.18.

The TPU elastomer has hard segments and soft segments, with cross-linksin the hard segments. The cross-links are the reaction product ofunsaturated bonds pendant from the hard segments, as catalyzed by afree-radical initiator.

The over-indexed cross-linked thermoplastic polyurethane elastomerprecursor is the reaction product formed from reacting

(a) a stoichiometric excess of at least about 1 mol percent of organicisocyanate moieties to the hydroxyl (or oxyhydrogen) moieties of theother reactants in the reaction product with a mixture of the followingreactants:

(b) an unsaturated diol, having two primary hydroxyl groups and at leastone allyl ether side group, of the formula

in which R¹ may be any substituted or unsubstituted alkyl, substitutedor unsubstituted aryl, substituted or unsubstituted alkyl-aryl group,substituted or unsubstituted ether group, substituted or unsubstitutedester group, any combination of the above groups, or H, and mayoptionally include an unsaturated bond in any main chain or side chainof any group; R² may be any suitable substituted or unsubstituted alkyl,substituted or unsubstituted aryl, substituted or unsubstitutedalkyl-aryl group, substituted or unsubstituted ether group, substitutedor unsubstituted ester group, any combination of the above groups; andR² includes an allyl group; and x and y are integers independentlyhaving any value from 1 to 10;

(c) a chain extender, having at least two reaction sites withisocyanates and having a molecular weight of less than about 450;

(d) a long chain polyol having a molecular weight of between about 500and about 4,000; and

(e) a sufficient amount of free radical initiator, so as to be capableof generating free radicals that induce cross-linking structures in thehard segments by free radical initiation.

The composition exhibits a dual cure phenomenon. A precursor compositionprovides a partial cure, and then the composition is moisture-cured toform a polyurethane/urea hybrid composition, which is the over-indexedcross-linked thermoplastic polyurethane elastomer disclosed herein.

Another aspect of the disclosure is directed to articles that require ascuff-resistant surface. Such articles, or the surfaces thereof, can bemade from the over-indexed, optionally cross-linked thermoplasticpolyurethane elastomer of the disclosure, just as with the method ofmaking golf balls disclosed herein.

In another aspect, this disclosure provides a method of making a golfball generally comprising the steps of forming a golf ball precursorhaving at least one preselected layer or piece but not an outer cover,and in particular comprising the steps of: forming an inner core layercomprising a highly neutralized acid polymer; forming an outer corelayer substantially surrounding the inner core layer; forming an innercover layer substantially surrounding the outer core layer to form anembodiment of a golf ball precursor; forming an outer cover layersubstantially surrounding the golf ball precursor or the inner coverlayer; and wherein the outer cover layer comprises a composition of anover-indexed thermoplastic polyurethane elastomer.

In yet another aspect the over-indexed thermoplastic polyurethaneelastomer used to form the outer cover layer includes cross-links, andparticularly cross-links formed from allyl ether side groups. Theover-indexed cross-linked thermoplastic polyurethane elastomer is thereaction product formed from reacting:

(a) a stoichiometric excess of at least about 1 mol percent of organicisocyanate moieties to the hydroxyl (or oxyhydrogen) moieties of theother reactants in the reaction product with a mixture of the followingreactants:

(b) an unsaturated diol, having two primary hydroxyl groups and at leastone allyl ether side group, of the formula

in which R¹ may be any substituted or unsubstituted alkyl, substitutedor unsubstituted aryl, substituted or unsubstituted alkyl-aryl group,substituted or unsubstituted ether group, substituted or unsubstitutedester group, any combination of the above groups, or H, and mayoptionally include an unsaturated bond in any main chain or side chainof any group; R² may be any suitable substituted or unsubstituted alkyl,substituted or unsubstituted aryl, substituted or unsubstitutedalkyl-aryl group, substituted or unsubstituted ether group, substitutedor unsubstituted ester group, any combination of the above groups; andR² includes an allyl group; and x and y are integers independentlyhaving any value from 1 to 10;

(c) a chain extender, having at least two reaction sites withisocyanates and having a molecular weight of less than about 450;

(d) a long chain polyol having a molecular weight of between about 500and about 4,000; and

(e) a sufficient amount of free radical initiator, so as to be capableof generating free radicals that induce cross-linking structures in thehard segments by free radical initiation to form a cover layercomprising over-indexed cross-linked thermoplastic polyurethaneelastomer precursor on the golf ball. The precursor then is treated withmoisture to cure the precursor and form an over-indexed cross-linkedthermoplastic polyurethane elastomer outer cover layer on the golf ball.

The disclosure also relates to golf balls made in accordance with thedisclosure. In embodiments of the present disclosure, the molar ratio ofthe organic isocyanate to the long chain polyol is greater than about1.01:1.00, typically greater than about 1.06:1.00.

Other systems, methods, features and advantages of the invention willbe, or will become, apparent to one of ordinary skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional systems, methods, features andadvantages be included within this description and this summary, bewithin the scope of the invention, and be protected by the followingclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawing and description. The components in the figure are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. Moreover, in the figure, like referencenumerals designate corresponding parts throughout the different views.

FIG. 1 shows a golf ball having aspects in accordance with thisdisclosure, the golf ball being of a two-piece construction;

FIG. 2 shows a second golf ball having aspects in accordance with thisdisclosure, the second golf ball having an inner cover layer and anouter cover layer;

FIG. 3 shows a third golf ball having aspects in accordance with thisdisclosure, the third golf ball having an inner core layer and an outercore layer; and

FIG. 4 shows a fourth golf ball having aspects in accordance with thisdisclosure, the four golf ball having an inner core layer, an outer corelayer, an inner cover layer, and an outer cover layer.

DETAILED DESCRIPTION

As used herein, unless otherwise stated, compression deformation,hardness, COR, flexural modulus, and Vicat softening temperature aremeasured as follows:

-   -   A. Compression deformation: The compression deformation herein        indicates the deformation amount of the ball, or any portion        thereof, under a force; specifically, when the force is        increased to become 130 kg from 10 kg, the deformation amount of        the ball or portion thereof under the force of 130 kg reduced by        the deformation amount of the ball or portion thereof under the        force of 10 kg is the compression deformation value of the ball        or portion thereof.    -   B. Hardness: Hardness of a golf ball layer is measured generally        in accordance with ASTM D-2240, but measured on the land area of        a curved surface of a molded ball.    -   C. Method of measuring COR: A golf ball for test is fired by an        air cannon at an initial velocity of 40 m/sec, and a speed        monitoring device is located over a distance of 0.6 to 0.9        meters from the cannon. The golf ball strikes a steel plate        positioned about 1.2 meters away from the air cannon and        rebounds through the speed-monitoring device. The return        velocity divided by the initial velocity is the COR.    -   D. Flexural modulus: Measured in accordance with ASTM D-790.    -   E. Vicat softening temperature: Measured in accordance with ASTM        D-1525.

Generally, this disclosure provides an over-indexed thermoplasticpolyurethane elastomer, and a method of making the over-indexedthermoplastic polyurethane elastomer. In some embodiments, thethermoplastic polyurethane elastomer is cross-linked, i.e., cross-linksare formed in the hard segments. The over-indexed, optionallycross-linked thermoplastic polyurethane composition exhibits a dual curephenomenon.

This disclosure also provides a method of making articles, particularlygolf balls, from the over-indexed, optionally cross-linked thermoplasticpolyurethane elastomer. In particular, in some embodiments relating togolf balls, the outer cover layer is made from the over-indexed,optionally cross-linked thermoplastic polyurethane. As a result of thedual cure phenomenon, the scuff resistance of a golf ball's outer cover,or of the outer surface of any article, may be greatly improved. Theover-indexed, cross-linked thermoplastic polyurethane elastomer exhibitssuperior scuff resistance.

The aspects of this disclosure that relate to use of over-indexed,optionally cross-linked thermoplastic polyurethane in a golf ball may beapplied to any golf ball precursor having any number of layers orpieces. The construction of a golf ball made according to the presentmethod is not limited to the embodiments mentioned with specificityherein. For example, a golf ball in accordance with this disclosure maygenerally take any construction, such as a regulation or non-regulationconstruction. Regulation golf balls are golf balls which meet the Rulesof Golf as approved by the United States Golf Association (USGA).

Thus, the disclosure herein can be applied to any of the ballsillustrated in FIGS. 1-4. For example, FIG. 1 shows a golf ball 100having a two-piece construction comprising core 120 and cover layer 110.FIG. 2 shows a second golf ball 200 having a three-piece constructioncomprising core 230, inner cover layer 220, and an outer cover layer210. FIG. 3 shows a third golf ball 300 having a three-piececonstruction comprising inner core layer 330, an outer core layer 320,and outer cover layer 310. FIG. 4 shows a fourth golf ball 400 havinginner core layer 440, outer core layer 430, inner cover layer 420, andouter cover layer 410. Typically, each layer essentially encompassesinterior layers.

The disclosure thus encompasses these golf balls, and golf balls having5 or more layers, or pieces. However, for convenience herein, thedisclosure will be directed to a four-piece, or four-layer, ball.

FIG. 4 shows a golf ball 400 made in accordance with the method of thepresent invention. Golf ball 400 includes an inner core layer 440, anouter core layer 430 substantially surrounding inner core layer 440, aninner cover layer 420 substantially surrounding outer core layer 430,and an outer cover layer 410 substantially surrounding inner cover layer420, wherein outer cover 410 comprises the over-indexed, optionallycross-linked, thermoplastic polyurethane elastomer disclosed herein.

In some embodiments of the present invention, outer cover layer 410 mayhave a material Shore D hardness (measured on a slab) of from about 30to about 45 and a ball surface Shore D hardness of from about 45 toabout 60. Typically, the ball surface Shore D hardness is from about 50to about 60, more typically from about 53 to about 57. In someembodiments of the present invention, outer cover layer 410 may have aball surface Shore C hardness of from about 70 to about 90. Typically,the ball surface Shore C hardness is from about 75 to about 85. Outercover layer 410 may have a flexural modulus of less than about 1,000psi, typically between about 400 psi and about 900 psi.

Both the over-indexed thermoplastic polyurethane elastomer and theover-indexed, cross-linked thermoplastic polyurethane elastomer mayinclude hard segments and soft segments, as thermoplastic polyurethanesare known to include. Thermoplastic polyurethanes are generally made upof (1) a long chain polyol, (2) a relatively short chain extender, and(3) a diisocyanate. Once reacted, the portions of the polymer chain madeup of the chain extender and diisocyanate generally align themselvesinto semi-crystalline structures through weak (i.e., non-covalent)association, such as through Van der Waals forces, dipole-dipoleinteractions or hydrogen bonding. These portions are commonly referredto as the hard segments, because the semi-crystalline structure isharder than the amorphous portions made up of the long chain polyol.

The over-indexed cross-linked thermoplastic polyurethane may includecross-links located specifically in the hard segments. These cross-linksmay be the reaction product of unsaturated bonds located in the hardsegments, as catalyzed by a free radical initiator. These unsaturatedbonds may be introduced into the hard segments by the use of unsaturateddiols as chain extenders. In particular embodiments, the cross-links maybe formed from allyl ether side groups present in the hard segments.

To form the over-indexed, optionally cross-linked thermoplasticpolyurethane elastomer, a precursor comprising a stoichiometric excessof isocyanate moieties is formed into the desired shape and then istreated with moisture to cure the precursor and form an over-indexed,optionally cross-linked thermoplastic polyurethane elastomer. Thus, anarticle can be fully cured in this way, and if the thermoplasticpolyurethane elastomer precursor is used to form an outer cover layer onthe golf ball, the thermoplastic polyurethane elastomer is formed inplace on the golf ball.

The above-mentioned chemical groups may have their conventionaldefinitions as is generally known in the art of chemistry. Specifically,an unsubstituted alkyl group includes any chemical group comprising onlycarbon and hydrogen linked by single bonds. A substituted alkyl groupmay include atoms other than carbon and hydrogen in a side chainportion, such as a halogen group, an inorganic group, or otherwell-known functional groups. In some embodiments, a substituted orunsubstituted alkyl group may include from 1 to about 100 carbon atomsin the alkyl chain. In other embodiments, a substituted or unsubstitutedalkyl group may have from 1 to 10 carbon atoms in the alkyl chain. Analkyl group, or any portion thereof, or alkyl substituent, may be astraight chain or branched.

As is further known in the art of chemistry, an aryl group is defined asany group that includes an aromatic benzene ring. Furthermore, analkyl-aryl group includes at least one aromatic benzene ring in additionto at least one alkyl carbon. An ether group includes at least oneoxygen atom bonded to two carbon atoms. An ester group includes at leastone carbon atom that is double bonded to a first oxygen atom and singlebonded to a second oxygen atom.

In some embodiments substituted groups, such as a substituted alkylgroup or a substitute aryl group, may be substituted with another of thesame group. For example, an alkyl may be substituted with another alkylto create a branched alkyl group. In other embodiments substitutedgroups may be substituted with a different group, for example an alkylmay be substituted with an ether group, or an ether group may besubstituted with an alkyl group. A person having ordinary skill in theart of chemistry may also synthesize suitable combinations of thesegroups, as may be desired.

The method of the present disclosure, and the products manufacturedtherefrom, include a molar ratio of the organic isocyanate moieties tothe hydroxyl (or oxyhydrogen) moieties of the other reactants is atleast about 1.01:1.00, typically at least about 1.06:1.00, moretypically from about 1.06:1.00 to about 1.18:1.00, or from about1.10:1.00 to about 1.15:1.00. The disclosure also contemplatesembodiments in which the molar ratio is from about 1.01:1.00 to about1.35:1.00, typically from about 1.06:1.00 to about 1.35:1.00, and moretypically from about 1.06:1.00 to about 1.25:1.00.

The skilled practitioner recognizes that this molar ratio of isocyanatemoieties to hydroxyl moieties is known as the “NCO index” or, simply,the Index. Thus, the molar ratio of 1.06:1.00 would be expressed as anindex of 1.06. The terms ‘index’ and ‘molar ratio’ are usedinterchangeably herein.

Additional cross-linking agents also may be incorporated in thethermoplastic polyurethane elastomer disclosed herein. These agents haveat least 2 functional groups. Each such unsaturated functional groupreacts with the unsaturated moieties in the unsaturated diol ofdifferent polyurethane molecules by free-radical or other polymerizationto cross-link the molecules.

Each of the above listed reactants will be discussed in further detail,with the understanding that any particular embodiment of a specificreactant may be mixed and matched with any other specific embodiment ofanother reactant according to the general formulation above.Furthermore, any reactant may generally be used in combination withother reactants of the same type, such that any list herein may beassumed to include mixtures thereof, unless otherwise specified.

The organic isocyanate may include any of the known aromatic, aliphatic,and cycloaliphatic di- or poly-isocyanates. Examples of suitableisocyanates include: 2,2′-, 2,4′- (and particularly)4,4′-diphenylmethane diisocyanate (MDI), and isomeric mixtures thereof;polyphenylene polymethylene polyisocyanates(poly-MDI, PMDI); 2,4- and2,6-toluene diisocyanates, and isomeric mixtures thereof such as an80:20 mixture of the 2,4- and 2,6-isomers (TDI); the saturated,isophorone diisocyanate; 1,4-diisocyanatobutane;1,5-diisocyanatopentane; 1,6-diisocyanatohexane; 1,4-cyclohexanediisocyanate; cycloaliphatic analogs of PMDI; and the like.

Suitable chain extenders may include the common diols, such as ethyleneglycol, diethylene glycol, triethylene glycol, propylene glycol,dipropylene glycol, tripropylene glycol, 1,3-propanediol,1,4-butanediol, 1,6-hexanediol, 1,10-decanediol, neopentyl glycol,dihydroxyethoxy hydroquinone, 1,4-cyclo-hexanedimethanol,1,4-dihydroxycyclohexane, and the like. Minor amounts of cross-linkingagents such as glycerine, trimethylolpropane, diethanolamine, andtriethanolamine may be used in conjunction with the diol chainextenders.

The skilled practitioner recognizes that the reaction product ofisocyanate and hydroxyl moieties is a urethane. However, isocyanate alsois reactive with amines, with the reaction product forming a urea.Therefore, in addition to the common diol chain extenders, diamines andamino alcohols may also be used to make over-indexed cross-linkedthermoplastic polyurethane elastomer. Examples of suitable diaminesinclude aliphatic, cycloaliphatic, or aromatic diamines. In particular,a diamine chain extender may be ethylene diamine, hexamethylene diamine,1,4-cyclohexylene diamine, benzidine, toluene diamine, diaminodiphenylmethane, the isomers of phenylene diamine or hydrazine. Aromatic aminesmay also be used, such as MOCA (4,4′-methylene-bis-o-chloroaniline),M-CDEA (4,4′-methylenebis(3-chloro-2,6-diethyl-aniline)). Examples ofsuitable amino alcohols, which can result in both urea and urethanestructures, include ethanol amine, N-methylethanolamine,N-butylethanolamine, N-oleylethanolamine, N-cyclohexylisopropanolamine,and the like. Mixtures of various types of chain extenders may also beused to form the cross-linked thermoplastic polyurethane.

The long chain polyol (“the polyol”) may generally be a polyester polyolor a polyether polyol. Accordingly, the over-indexed cross-linkedthermoplastic polyurethane may be either general type of polyurethane: apolyether-based polyurethane elastomer or a polyester-based polyurethaneelastomer, or mixtures thereof.

The long chain polyol may be a polyhydroxy compound having a molecularweight between 500 and 4,000. Suitable long chain polyols may generallyinclude linear polyesters, polyethers, polycarbonates, polylactones(e.g., c-caprolactone), and mixtures thereof. In addition to polyolshaving hydroxyl terminal groups, the polyol may include carboxyl, aminoor mercapto terminal groups.

Polyester polyols are produced by the reaction of dicarboxylic acids anddiols or an esterifiable derivative thereof. Examples of suitabledicarboxylic acids include succinic acid, glutaric acid, adipic acid,suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid,maleic acid, fumaric acid, phthalic acid, isophthalic acid, andterephthalic acid. Examples of suitable diols include ethanediol,diethylene glycol, 1,2- and 1,3-propanediol, dipropylene glycol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol,glycerine and trimethylolpropanes, tripropylene glycol, tetraethyleneglycol, tetrapropylene glycol, tetramethylene glycol,1,4-cyclohexane-dimethanol, and the like. Both of the dicarboxylic acidsand diols can be used individually or in mixtures to make specificpolyesters in the practice applications.

Polyether polyols are prepared by the ring-opening additionpolymerization of an alkylene oxide with an initiator of a polyhydricalcohol. Examples of suitable polyether polyols are polypropylene glycol(PPG), polyethylene glycol (PEG), polytetramethylene ether glycol(PTMEG). Block copolymers such as combinations of polyoxypropylene andpolyoxyethylene glycols, poly-1,2-oxybutylene and polyoxyethyleneglycols, poly-1,4-tetramethylene and polyoxyethylene glycols are alsopreferred in the present invention.

Polycarbonate polyols are made through a condensation reaction of diolswith phosgene, chloroformic acid ester, dialkyl carbonate or diallylcarbonate. Examples of diols in the suitable polycarbonate polyols ofthe cross-linked thermoplastic polyurethane elastomers are ethanediol,diethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol,neopentylglycol, and 1,5-pentanediol.

Additional di- or multi-functional cross-linking agents also may beincluded in the thermoplastic polyurethane elastomer. One class ofsuitable compounds is diacrylates, particularly diacrylates havingterminal unsaturation. One such compound is 1,6-hexanediol diacrylate, acommercially-available product. Other similar diacrylates also aresuitable.

The over-indexed cross-linked thermoplastic polyurethane elastomer maycomprise a sufficient amount of free radical initiator so as to becapable of inducing cross-linking structures in the hard segments byfree radical initiation at the unsaturated moiety. The free radicalinitiator may generate free radicals through thermal cleavage or UVradiation. When the half-life of the free radical initiator and itsoperation temperature are considered in the manufacturing process, theweight ratio of initiators to unsaturated diols may be from 100:0.1 to100:100. In particular embodiments, the weight ratio of free radicalinitiator to unsaturated diols may be about 5:100.

A variety of known free radical initiators may be used as the radicalsource in order to make the over-indexed cross-linked polyurethaneelastomer having a cross-linked structure. Suitable radical initiatorsmay include peroxides, sulfurs, and sulfides, and peroxides may beparticularly suitable in some embodiments. The peroxides may bealiphatic peroxides or and aromatic peroxides, or mixtures thereof.Aromatic peroxides, such as diacetylperoxide, di-tert-butylperoxide,dicumylperoxide, dibenzoylperoxide,2,5-dimethyl-2,5-di(benzoylperoxy)hexane,2,5-dimethyl-2,5-di(butylperoxy)-3-hexyne,2,5-bis-(t-butylperoxy)-2,5-dimethyl hexane,n-butyl-4,4-bis(t-butylperoxyl)valerate,1,4-bis-(t-butylperoxyisopropyl)-benzene, t-butyl peroxybenzoate,1,1-bis-(t-butylperoxy)-3,3,5 tri-methylcyclohexane, anddi(2,4-dichloro-benzoyl) may be used as the free radical initiator insome embodiments. The skilled practitioner recognizes that the freeradical initiators begin to act at different temperatures. For example,dicumyl peroxide begins initiation at a higher temperature than doesbenzoyl peroxide. With the guidance provided herein, the skilledpractitioner will be able to select a suitable initiator.

If the thermoplastic polyurethane elastomer is to be cross-linked, anunsaturated diol may generally be any diol having at least oneunsaturated bond. As is generally known, an unsaturated bond may be adouble bond between two carbon atoms (as in an alkene) or a triple bond(as in an alkyne). In particular embodiments, the unsaturated diol mayhave two primary alcohol groups. The presence of two primary alcoholgroups may result in favorable reaction kinetics, such that thecross-linked thermoplastic polyurethane may be formed in an easilycontrolled “one step” continuous process.

In particular embodiments, the unsaturated diol may have two primaryhydroxyl groups and at least one allyl ether side group, so as to be ofthe formula:

in which R is alkyl group with or without modified functional groups,and x and y are integers of 1 to 4. In particular embodiments, x and ymay both have values of 1, 2, 3 or 4. In other embodiments, x and y mayeach have different values of between 1 and 4.

In one particular embodiment, the unsaturated diol may betrimethylolpropane monoallylether (“TMPME”). TMPME may also be named“trimethylol propane monoallyl ether”, “trimethylol propanemonoallylether”, or “trimethylolpropane monoallyl ether.” TMPME has CASno. 682-11-1. TMPME may also be referred to as 1,3-Propanediol,2-ethyl-2-[(2-propen-1-yloxy)methyl] or as2-allyloxymethyl-2-ethyl-1,3-propanediol. TMPME is commerciallyavailable from Perstorp Specialty Chemicals AB.

Other suitable compounds that may be used as the unsaturated diol offormula (I) may include: 1,3-Propanediol,2-(2-propen-1-yl)-2-[(2-propen-1-yloxy)methyl]; 1,3-Propanediol,2-methyl-2-[(2-propen-1-yloxy)methyl]; 1,3-Propanediol,2,2-bis[(2-propen-1-yloxy)methyl; and 1,3-Propanediol,2-[(2,3-dibromopropoxy)methyl]-2-[(2-propen-1-yloxy)methyl]. Furthercompounds within the scope of formula (I) may be known to a personhaving ordinary skill in the art, and may be used in the presentinvention.

The weight ratio of cross-linked thermoplastic polyurethane elastomer tothe unsaturated diols may generally be from about 100:0.1 to about100:25. In particular embodiments, the weight ratio of cross-linkedthermoplastic polyurethane elastomer to the unsaturated diols may beabout 100:10.

The inventors have discovered that a stoichiometric excess of isocyanatemoieties of at least about 1 mol percent, and typically at least about 6mol percent, yields a product that resists shear failure yet remains aTPU elastomer. Thus, the over-indexed, optionally cross-linked TPUelastomer described herein is particularly suitable for thermoforming,such as forming a cover on an article or an outer cover layer on a golfball. The outer cover layer thus would resist stress failure thattypically manifests itself as corrugations or ‘hairs’ on the surface ofthe golf ball. Thus, golf ball covers and other surfaces that requirestress resistance, such as livestock tags, shoe bindings, and furniture,also are suitably made with such material.

The index of over-indexed, optionally cross-linked TPU elastomer inembodiments herein is at least about 1.01, typically is at least about1.06, more typically is between about 1.06 and 1.18, and more typicallybetween about 1.10 and about 1.15. In other embodiments, the index isbetween about 1.01 and 1.35, typically between about 1.06 and 1.35, andmore typically between about 1.06 and 1.25. A large excess ofisocyanate, for example, an index greater than about 1.35, typically isa waste of reactant and leaves unreacted isocyanate, which is a sourceof unintended reactions that may form corrosive and dangerous materials,even after the second curing step.

Optionally, the over-indexed, optionally cross-linked thermoplasticpolyurethane elastomer may include further components such as fillersand/or additives. Fillers and additives may be used based on any of avariety of desired characteristics, such as enhancement of physicalproperties, UV light resistance, and other properties. For example, toimprove UV light resistance, the over-indexed cross-linked thermoplasticpolyurethane elastomer may include at least one light stabilizer. Lightstabilizers may include hindered amines, UV stabilizers, or a mixturethereof.

Inorganic or organic fillers can be also added to the over-indexedcross-linked thermoplastic polyurethane elastomer. Suitable inorganicfillers may include silicate minerals, metal oxides, metal salts, clays,metal silicates, glass fibers, natural fibrous minerals, syntheticfibrous minerals or a mixture thereof. Suitable organic fillers mayinclude carbon black, fullerene and/or carbon nanotubes, melaminecolophony, cellulose fibers, polyamide fibers, polyacrylonitrile fibers,polyurethane fibers, polyester fibers based on aromatic and/aliphaticdicarboxylic acid esters, carbon fibers or a mixture thereof. Theinorganic and organic fillers may be used individually or as a mixturethereof. The total amount of the filler may be from about 0.5 to about30 percent by weight of the polyurethane components.

Flame retardants may also be used to improve the flame resistance of theover-indexed cross-linked thermoplastic polyurethane elastomer. Suitableflame retardants may include organic phosphates, metal phosphates, metalpolyphosphates, metal oxides (such as aluminum oxide hydrate, antimonytrioxide, arsenic oxide), metal salts (such as calcium sulfate,expandable graphite), and cyanuric acid derivatives (such as melaminecyanurate). These flame retardants may be used individually or as amixture thereof, and the total amount of the flame retardant may be fromabout 10 to about 35 percent by weight of the polyurethane components.

To improve toughness and compression rebound, the cross-linkedthermoplastic polyurethane elastomer may include at least onedispersant, such as a monomer or oligomer comprising unsaturated bonds.Examples of suitable monomers include styrene, acrylic esters; suitableoligomers include di- and tri-acrylates/methacrylates, esteracrylates/methacrylates, and urethane or urea acrylates/methacrylates.When a diacrylate-containing compound is used as a dispersant, it alsomay enter into the cross-linking reaction.

If the outermost layer of a golf ball, or the outer surface of anarticle, comprises the over-indexed cross-linked thermoplasticpolyurethane elastomer, then the cross-linked thermoplastic polyurethaneelastomer may include at least one white pigment to aid in bettervisibility. The white pigment may be selected from the group consistingof titanium dioxide, zinc oxide or a mixture thereof. Pigments of othercolors may serve equally well, particularly in other articles, such assports balls or livestock tags, for color-coding the articles, toincrease visibility, or to increase the legibility of text printedthereon. With the guidance provided herein, the skilled practitioner canidentify suitable additives.

The over-indexed, optionally cross-linked thermoplastic polyurethaneelastomer may generally be formed by a single-screw, twin-screw, or abatch method in order to mix and react all of the ingredients describedabove. The products of the reaction process may be in the form ofpellets or ground chips.

Over-indexed thermoplastic polyurethane elastomer precursor andover-indexed cross-linked thermoplastic polyurethane elastomer precursorcan be made in any way that yields a TPU having an excess of isocyanatemoieties sufficient to meet the NCO index available for a cure step inwhich the TPU is exposed to moisture. One method is to mix all reactantsin, for example, a screw extruder and then to form small pieces, such aspellets. The pellets may be processed in any way that preserves theunreacted isocyanate moieties by limiting moisture to less than about3,000 ppm, typically less than about 2,000 ppm, more typically less thanabout 1,000 ppm, and even more typically less than about 800 ppm, untilthe pellets are used, such as in an injection molding step, to form aportion, typically the cover, of the golf ball. After forming the golfball, or any other object, the moisture-curing step then forms thepolyurethane/polyurea hybrid that is the over-indexed, optionallycross-linked, thermoplastic polyurethane elastomer. One such method isdisclosed in U.S. Application Ser. No. 61/582,658, (PLG Docket 72-1513),filed on even date herewith.

The over-indexed, optionally cross-linked thermoplastic polyurethaneelastomer of the disclosure may be used to make golf balls by injectionmolding or compression molding. Other articles can be made in the sameway. Injection molding may be used in particular embodiments in order toachieve increased productivity. Generally, the free radical initiatormay be added to the polymer mixture at any of several stages duringmanufacturing. For example, the free radical initiator may be addedduring extrusion of the polymer mixture, or during compression molding.Similarly, the free radical initiator may be activated so as to formcross-links during any of several stages of manufacturing. For example,the free radical initiator may be activated by heating during anextrusion process.

For any ball layer(s) other than the layer(s) comprising theover-indexed, optionally cross-linked thermoplastic polyurethaneelastomer, suitable materials can be selected from any of the variousmaterials known to be used in golf ball manufacturing. Specifically,such other materials may be selected from the following groups: (1)thermoplastic materials selected from the group consisting of ionomerresin, highly neutralized acid polymer composition, polyamide resin,polyester resin, polyurethane resin and a mixture thereof; or (2)thermoset materials selected from the group consisting of polyurethaneelastomer, polyamide elastomer, polyurea elastomer, diene-containingpolymer (such as polybutadiene), cross-linked metallocene catalyzedpolyolefin, silicone, and a mixture thereof.

For example, in embodiments where the core construction is multilayered,the choice of the material making up the core layer or the inner corelayer, such as inner core layer 330 or 440 (as shown in FIG. 3 or 4,respectively) is not particularly limited. The material making up theinner core layer may be selected from the following groups: (1)thermoplastic materials selected from the group consisting of ionomerresin, highly neutralized acid polymer composition, polyamide resin,polyester resin, polyurethane resin and a mixture thereof; or (2)thermoset materials selected from the group consisting of polyurethaneelastomer, polyamide elastomer, polyurea elastomer, diene-containingpolymer (such as polybutadiene), cross-linked metallocene catalyzedpolyolefin, silicone, and a mixture thereof.

Among the various thermoplastic and thermoset materials, inner corelayer 440 may comprise ionomer resin or highly neutralized acid polymercomposition in particular embodiments. For example, Surlyn®, HPF 1000,HPF 2000, HPF AD1027, HPF AD1035, HPF AD1040, and a mixture thereof, allproduced by E. I. DuPont de Nemours and Company, may be used. In someembodiments, inner core layer 440 may comprise highly neutralized acidpolymer composition (HNP). In particular, to enable a broader range ofproperties and characteristics of the golf ball precursor, two or moreHNPs may be used, typically as a mixture. The highly neutralized acidpolymer composition(s) of inner core layer 440 have Vicat softeningtemperatures of from 50° C. to 60° C.

Suitable highly neutralized acid polymer compositions for use in forminginner core layer 440 may comprise a highly neutralized acid polymercomposition and optionally additives, fillers, and/or melt flowmodifiers. The acid polymer is neutralized to 70% or higher, includingup to 100%, with a suitable cation source, such as magnesium, sodium,zinc, or potassium.

Suitable additives and fillers include, for example, blowing and foamingagents, optical brighteners, coloring agents, fluorescent agents,whitening agents, UV absorbers, light stabilizers, defoaming agents,processing aids, mica, talc, nanofillers, antioxidants, stabilizers,softening agents, fragrance components, plasticizers, impact modifiers,acid copolymer wax, surfactants; inorganic fillers, such as zinc oxide,titanium dioxide, tin oxide, calcium oxide, magnesium oxide, bariumsulfate, zinc sulfate, calcium carbonate, zinc carbonate, bariumcarbonate, mica, talc, clay, silica, lead silicate, and the like; highspecific gravity metal powder fillers, such as tungsten powder,molybdenum powder, and the like; regrind, i.e., inner core material thatis ground and recycled; and nano-fillers. Suitable melt flow modifiersinclude, for example, fatty acids and salts thereof, polyamides,polyesters, polyacrylates, polyurethanes, polyethers, polyureas,polyhydric alcohols, and combinations thereof.

Inner core layer 440 may be made by a fabrication method such ashot-press molding or injection molding. In embodiments of thedisclosure, the diameter of inner core layer 440 may be in a range ofabout 21 millimeters to about 28 millimeters, or in a range of about 24millimeters to about 28 millimeters. Inner core layer 440 may have asurface Shore D hardness of 45 to 55. Inner core layer 440 has a Shore Dcross-sectional hardness of from 45 to 55 at any single point on across-section obtained by cutting inner core layer 440 in half, and hasa Shore D cross-sectional hardness difference between any two points onthe cross-section of within ±6. By controlling the Shore D hardnessdifference of inner core layer 440, the ball over-all performance may bestable. To have a lower ball spin rate, inner core layer 440 may have acompression deformation of from about 3.4 millimeters to about 4.2millimeters.

To protect thermoplastic inner core layer 440 during core-formingprocess, it is preferred that outer core layer 430 has a thickness offrom 5 millimeters to 9 millimeters and has a volume which is greaterthan any other layers of golf ball 400. Outer core layer 430 typicallyhas a surface Shore D hardness of between about 50 to about 60, and thehardness of the outer core layer is greater than the Shore D hardness ofinner core layer 440.

The material making up outer core layer 430 may be thermoset materialsselected from the group consisting of polyurethane elastomer, polyamideelastomer, polyurea elastomer, diene-containing polymer (such aspolybutadiene), cross-linked metallocene catalyzed polyolefin, silicone,and a mixture thereof. Outer core layer 430 may be made by cross-linkinga polybutadiene rubber composition. When other rubber is used incombination with a polybutadiene, it is preferred that polybutadiene isincluded as a principal component. Specifically, a proportion ofpolybutadiene in the entire base rubber is preferably equal to orgreater than about 50 percent by weight, and particularly preferablyequal to or greater than about 80 percent by weight. A polybutadienehaving a proportion of cis-1,4 bonds of equal to or greater than about60 mol percent, and further, equal to or greater than about 80 molpercent, is preferred.

In some embodiments, cis-1,4-polybutadiene may be used as the baserubber and mixed with other ingredients. In some embodiments, the amountof cis-1,4-polybutadiene may be at least about 50 parts by weight, basedon 400 parts by weight of the rubber compound. Various additives may beadded to the base rubber to form a compound. The additives may include across-linking agent and a filler. In some embodiments, the cross-linkingagent may be zinc diacrylate, magnesium acrylate, zinc methacrylate, ormagnesium methacrylate. In some embodiments, zinc diacrylate may provideadvantageous resilience properties. The filler may be used to increasethe specific gravity of the material. The filler may include zinc oxide,barium sulfate, calcium carbonate, or magnesium carbonate. In someembodiments, zinc oxide may be selected for its advantageous properties.Metal powder, such as tungsten, may alternatively be used as a filler toachieve a desired specific gravity. In some embodiments, the specificgravity of outer core layer 430 may be from about 1.05 g/cm³ to about1.25 g/cm³. Further, outer core layer 430 may have a surface Shore Dhardness of from about 30 to about 75.

In some embodiments, a polybutadiene synthesized using a rare earthelement catalyst is preferred. By using this polybutadiene, excellentresilience performance of golf ball 400 can be achieved. Examples ofrare earth element catalysts include lanthanum series rare earth elementcompound, organoaluminum compound, and alumoxane and halogen containingcompound. A lanthanum series rare earth element compound is preferred.Polybutadiene obtained by using lanthanum rare earth-based catalystsusually employ a combination of lanthanum rare earth (atomic number of57 to 71) compounds, but particularly preferred is a neodymium compound.

Outer core layer 430 is preferably made by hot-press molding process.Suitable vulcanization conditions include a vulcanization temperature ofbetween 130° C. and 190° C. and a vulcanization time of between 5 and 20minutes. To obtain the desired rubber cross-linked body for use as thecore in the present invention, the vulcanizing temperature is preferablyat least 140° C.

When outer core layer 430 of the present invention is produced byvulcanizing and curing the rubber composition in the above-describedway, advantageous use may be made of a method in which the vulcanizationstep is divided into two stages. The outer core layer material is placedin an outer core layer-forming mold and subjected to initialvulcanization so as to produce a pair of semi-vulcanized hemisphericalcups, and then a prefabricated inner core layer is placed in one of thehemispherical cups and is covered by the other hemispherical cup, inwhich state complete vulcanization is carried out.

The surface of inner core layer 440 placed in the hemispherical cups maybe roughened before the placement to increase adhesion between innercore layer 440 and outer core layer 430. In some embodiments, inner corelayer surface is pre-coated with an adhesive or pre-treated withchemical(s) before placing inner core layer 440 in the hemisphericalcups to enhance the durability of the golf ball and enable a highrebound.

Alternatively, the inner core layer may comprise the aforementionedthermoset material while the outer core layer may comprise thethermoplastic material, or any combination thereof.

In embodiments where the core construction is multilayered, the COR ofthe inner core layer, such as inner core layer 440 in FIG. 1, at forty(40) meters per second may be from about 0.78 to about 0.92, and may behigher than that of the golf ball as a whole. In other embodiments, theCOR of the golf ball at forty (40) meters per second may be at leastabout 0.77.

In a particular embodiment of this disclosure relating to a four-piecegolf ball, inner core layer 440 has a COR value from 0.785 to 0.9,preferably from 0.795 to 0.89, more preferably from 0.8 to 0.88. Innercore layer 440 has a first coefficient of restitution, and golf ball 400has a second coefficient of restitution, and the first coefficient ofrestitution is higher than the second coefficient of restitution by atleast 0.01. Golf ball 400 of the present invention has a coefficient ofrestitution of at least 0.775.

Inner cover layer 420 of the golf ball described herein may comprise athermoplastic material. The thermoplastic material of inner cover layer420 comprises at least one of an ionomer resin, a highly neutralizedacid polymer composition, a polyamide resin, a polyurethane resin, apolyester resin, or a combination thereof. In some embodiments, innercover layer 420 comprises the same type of over-indexed, optionallycross-linked thermoplastic polyurethane as outer cover layer 410. Insome embodiments, inner cover layer 420 also may comprise a cross-linkedbut not over-indexed polyurethane, or may comprise yet anotheruncross-linked thermoplastic polyurethane different from outer coverlayer 410, while in some embodiments, inner cover layer 420 comprises adifferent material from outer cover layer 410.

In embodiments of the disclosure, inner cover layer 420 has a thicknessof less than about 2 millimeters. In some embodiments, inner cover layer420 of the present invention has a thickness of less than about 1.5millimeters. In some embodiments, inner cover layer 420 of the presentinvention has a thickness of less than about 1 millimeter. Althoughinner cover layer 420 is relatively thin compared to the rest of thelayers of golf ball 400, it has the highest surface Shore D hardnessamong all layers. In some embodiments, inner cover layer 420 has asurface Shore D hardness of from about 60 to about 70 as measured on thecurved surface. Also, inner er layer 420 has a high flexural modulus offrom about 60,000 psi to about 100,000 psi, or from about 70,000 psi toabout 85,000 psi. In some embodiments, the specific gravity of innercover layer 420 may be from about 1.05 g/cm³ to about 1.5 g/cm³ tocreate a greater moment of inertia.

The compositions of this disclosure are subjected to a dual-curingprocess. The composition is chemically-cured when it is reacted with thediol chain extenders. Then, the resulting composition is moisture-curedin accordance with the steps described below.

The above-described chemical curing mechanism provides an over-indexed,optionally cross-linked thermoplastic polyurethane elastomer, whichsubsequently is fully-cured by contacting the composition with moisture.The resulting fully-cured composition has improved scuff resistanceperformance. Different methods may be used for applying the moisture tothe composition in the moisture-curing step. For example, thepartially-cured composition formed by the chemical-curing step simplymay be exposed to ambient moisture for a sufficient period to fully-curethe material. Alternatively, a spray of moisture may be applied to thecomposition so that it fully cures. In another embodiment, a compositionis soaked in hot water for one to two hours. In yet another embodiment,the composition is placed in a humidity chamber at relatively highhumidity (particularly, the relative humidity is at least 50%.)Preferably, the humidity chamber has a temperature of 70° C., a relativehumidity (RH) of 90%, and the composition is placed in the chamber forone to two hours to achieve good curing of the composition in arelatively short period.

EXAMPLES

Two golf balls in accordance with the present invention were fabricatedas described below, and their scuff resistance was compared to severalcomparative examples.

For each golf ball, the inner core layer was made from a materialselected from Table 1, the outer core layer was made from a materialselected from Table 2, the inner cover layer was made from a materialselect from Table 3, and the cover layer was made from a materialselected from Table 4. The amount of the materials listed in Tables 1,2, 3 and 4 is shown in parts by weight (pbw) or percentages by weight.

TABLE 1 Inner Core Materials Resin: A B HPF 2000* 78 0 HPF AD 1035* 22100 *HPF 2000 and HPF AD 1035 are trade names of ionomeric resins by E.I. DuPont de Nemours and Company.

TABLE 2 Outer Core Material Rubber compound: C D TAIPOL ™ BR0150* 100100 Zinc diacrylate 29 29 Zinc oxide 9 9 Barium sulfate 11 9 Peroxide 11 *TAIPOL ™ BR0150 is the trade name of a rubber produced by TaiwanSynthetic Rubber Corp.

TABLE 3 Inner Cover Material Resin: E Neothane 6303D* 100 *Neothane6303D is the trade name of a thermoplastic polyurethane produced byDongsung Highchem Co. LTD.

TABLE 4 Outer Cover Materials F G H I J PTMEG (pbw) 100 100 100 100 100BG (pbw) 15 15 15 15 15 TMPME (weight % to 10% 10% 0 10% 10% totalcomponents) DCP (weight % to 0.5%  0.5%  0 0 0 total components) MDI(pbw) 92.1 102.6 55.0 92.1 102.6 Molar ratio of organic 1.06:1.001.18:1.00 1.01:1.00 1.06:1.00 1.18:1.00 isocyanate to oxy- hydrogen(hydroxyl)

“PTMEG” is polytetramethylene ether glycol, having a number averagemolecular weight of 2,000, and is commercially available from Invista,under the trade name of Terathane® 2000. “BG” is 1,4-butanediol,commercially available from BASF and other suppliers. “TMPME” istrimethylolpropane monoallylether, commercially available from PerstorpSpecialty Chemicals AB. “DCP” is dicumyl peroxide, commerciallyavailable from LaPorte Chemicals Ltd. “MDI” is diphenylmethanediisocyanate, commercially available from Huntsman, under the trade nameof Suprasec® 1100.

Outer cover materials F, G, H, I and J were formed by mixing PTMEG, BG,TMPME, DCP and MDI in the proportions shown. Specifically, thesematerials were prepared by mixing the components in a highly agitatedstirrer for 1 minute, starting at a temperature of about 70° C.,followed by a 10-hour post curing process at a temperature of about 100degrees Celsius. The post cured polyurethane elastomers were ground intosmall chips. The manufacturing process maintained low moisture levels,including less than about 800 ppm after cooling and comminution, andless than about 300 ppm after secondary drying as described above.

From the above materials, five kinds of golf balls were manufactured, asshown in Table 5. Generally, the golf balls were manufactured usingconventional compression molding and injection molding processes knownin the art of golf ball manufacturing. After all golf balls were made,all golf balls were kept in an environment with a temperature of 30° C.and a relative humidity of 50 percent for 4 hours.

TABLE 5 Golf Ball Testing Data Examples Comparative examples 1 2 3 4 5Inner Core Layer Material A B A B A Diameter (mm) 24 21 24 21 24 Shore DHardness 53 46 53 46 53 Compression 3.2 4.2 3.2 4.2 3.2 Deformation (mm)COR 0.83 0.81 0.83 0.81 0.83 Outer Core Layer Material C D C D CThickness (mm) 7.25 8.75 7.25 8.75 7.25 Shore D Hardness 59 58 59 58 59Inner Cover Layer Material E E E E E Thickness (mm) 1.0 1.0 1.0 1.0 1.0Shore D Hardness 69 68 69 68 69 Flexural Modulus 77,000 77,000 77,00077,000 77,000 (psi) Outer cover layer Resin F G H I J Thickness (mm) 1.11.1 1.1 1.1 1.1 Shore D Hardness 53 52 53 52 53 Flexural Modulus 550 530480 490 490 (psi) Ball COR 0.785 0.775 0.785 0.775 0.785 ScuffResistance Rating 2.5 1.5 4 3.5 3

A scuff resistance test was conducted in the following manner: a NikeVictory Red forged standard sand wedge (loft: 54′; bounce: 12′; shaft:True Temper Dynamic Gold shaft; flex: S) is fixed to a swing robotmanufactured by Miyamae Co., Ltd. and then swung at the head speed ofabout 32 m/s. The club face was oriented for a square hit. Theforward/backward tee position was adjusted so that the tee was fourinches behind the point in the downswing where the club was vertical.The height of the tee and the toe-heel position of the club relative tothe tee were adjusted in order that the center of the impact mark wasabout ¾ of an inch above the sole and was centered toe to heel acrossthe face. Three samples of each ball were tested. Each ball was hitthree times.

Other methods may also be used to determine the scuff resistance, suchas the methods described in the commonly assigned copending applicationtitled “Golf Ball Wear Indicator”, U.S. application Ser. No. 12/691,282,filed Jan. 21, 2010, in the name of Brad Tutmark.

After the above described scuff resistance testing, each golf ball coverwas visually observed and rated according to the following scale: a golfball cover was rated “1” when little or no damage was visible, onlygroove markings or dents; a golf ball cover was rated “2” when smallcuts and/or ripples in the cover were apparent; a golf ball cover wasrated “3” when moderate amounts of cover material were lifted from theball's surface, but the cover material was still attached to the ball;and finally a golf ball cover was rated “4” when cover material wasremoved or barely attached to the golf ball.

Shore D hardness values of the core and cover layer were measured on thespherical surface of the layer to be measured by using a Shore Dhardness tester.

As shown in Table 5, golf ball examples 1 and 2 made from compositionsincluding a cross-linked thermoplastic polyurethane elastomer havingcross-links located in the hard segments, where the cross-links are thereaction product of unsaturated bonds located in the hard segments ascatalyzed by a free radical initiator and a proper ratio of the organicisocyanate to the long chain polyol, provides superior scuff resistance.

Additional golf balls are made in accordance with the method andcomprising the compositions of Examples 1 and 2, with the exception thatthe index is 1.20 in one golf ball, 1.30 in another, and 1.40 in athird. The golf balls then are subjected to the scuffing test, andprovide a scuff resistance rating of 1.5, 1.5, and 1.

While various embodiments of the invention have been described, thedescription is intended to be exemplary, rather than limiting and itwill be apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible that are within the scopeof the invention. Accordingly, the invention is not to be restrictedexcept in light of the attached claims and their equivalents. Also,various modifications and changes may be made within the scope of theattached claims. For example, different golf ball precursors, perhapsthose having a different number of layers or a different corecomposition, also fall within the scope of the claims.

We claim:
 1. A method of making a golf ball, comprising the steps of:forming a golf ball precursor, the precursor having at least 1 golf balllayer but not an outer cover layer; and forming an outer cover layersubstantially surrounding the golf ball precursor; and wherein the outercover layer comprises a composition of an over-indexed, cross-linkedthermoplastic polyurethane elastomer including cross-links formed fromallyl ether side groups, and the cross-linked thermoplastic polyurethaneelastomer being the reaction product formed from reacting: (a) astoichiometric excess of at least about 1 mol percent of organicisocyanate moieties to the hydroxyl (or oxyhydrogen) moieties of theother reactants in the reaction product with a mixture of the followingreactants: (b) an unsaturated diol, having two primary hydroxyl groupsand at least one allyl ether side group, of the formula

in which R¹ may be any substituted or unsubstituted alkyl, substitutedor unsubstituted aryl, substituted or unsubstituted alkyl-aryl group,substituted or unsubstituted ether group, substituted or unsubstitutedester group, any combination of the above groups, or H, and mayoptionally include an unsaturated bond in any main chain or side chainof any group; R² may be any suitable substituted or unsubstituted alkyl,substituted or unsubstituted aryl, substituted or unsubstitutedalkyl-aryl group, substituted or unsubstituted ether group, substitutedor unsubstituted ester group, any combination of the above groups; andR² includes an allyl group; and x and y are integers independentlyhaving any value from 1 to 10; (c) a chain extender, having at least tworeaction sites with isocyanates and having a molecular weight of lessthan about 450; (d) a long chain polyol having a molecular weight ofbetween about 500 and about 4,000; and (e) a sufficient amount of freeradical initiator, so as to be capable of generating free radicals thatinduce cross-linking structures in the hard segments by free radicalinitiation.
 2. The method of making the golf ball according to claim 1,wherein the molar ratio of the organic isocyanate moieties to thehydroxyl moieties of the other components is from about 1.06:1.00 toabout 1.18:1.00, further comprising curing the composition in a dualcuring phenomena by applying the composition over the golf ballprecursor and allowing it to partially-cure, and then moisture-curingthe composition to form an outer cover layer comprising apolyurethane/urea hybrid composition.
 3. The method of making the golfball according to claim 2, wherein the molar ratio is from about1.10:1.00 to about 1.15:1.00.
 4. The method of making the golf ballaccording to claim 1, wherein the free radical initiator is present inthe cross-linked thermoplastic polyurethane elastomer in a weight ratioof free radical initiator to unsaturated diols of from about 0.1:100 toabout 100:100.
 5. The method of making the golf ball according to claim4, wherein a weight ratio of the cross-linked thermoplastic polyurethaneelastomer to the unsaturated diols is about 100:10.
 6. The method ofmaking the golf ball according to claim 1, wherein the unsaturated diolis trimethylolpropane monoallylether.
 7. The method of making the golfball according to claim 1, wherein the free radical initiator generatesfree radicals through at least one of thermal cleavage and UV radiation.8. The method of making the golf ball according to claim 1, wherein thefree radical initiator is selected from the group consisting ofperoxides, sulfurs, and sulfides.
 9. The method of making the golf ballaccording to claim 1, wherein the step of forming a golf ball precursorfurther comprises the steps of: forming an inner core layer comprising ahighly neutralized acid polymer; forming an outer core layersubstantially surrounding the inner core layer; and forming an innercover layer substantially surrounding the outer core layer.
 10. A methodof making a golf ball comprising the steps of forming a golf ballprecursor, the precursor having at least 1 golf ball layer but not anouter cover layer; and forming an outer cover layer substantiallysurrounding the precursor, the outer cover layer comprising acomposition of an over-indexed thermoplastic polyurethane elastomerhaving an NCO index of from about 1.01 to about 1.35.
 11. The method ofmaking the golf ball of claim 10, further comprising curing thecomposition in a dual curing phenomena by applying the composition overthe golf ball precursor and allowing it to partially-cure, and thenmoisture-curing the composition to form an outer cover layer comprisinga polyurethane/urea hybrid composition.
 12. The method of making thegolf ball according to claim 10, wherein the NCO index is from about1.06 to about 1.35.
 13. The method of making the golf ball according toclaim 12, further comprising curing the composition in a dual curingphenomena by applying the composition over the golf ball precursor andallowing it to partially-cure, and then moisture-curing the compositionto form an outer cover layer comprising a polyurethane/urea hybridcomposition.
 14. A golf ball comprising at least 1 golf ball layersubstantially surrounded by an outer cover layer, the outer cover layercomprising a polyurethane/urea hybrid comprising the reaction product ofwater and an over-indexed thermoplastic polyurethane elastomer having anNCO index of between about 1.06 and about 1.18.
 15. The golf ballaccording to claim 14, wherein the at least 1 golf ball layer comprisesa core and an outer core layer.
 16. The golf ball according to claim 14,wherein the at least 1 golf ball layer comprises a core and an innercover layer.
 17. A golf ball comprising at least 1 golf ball layersubstantially surrounded by an outer cover layer, the outer cover layercomprising a thermoplastic polyurethane elastomer cross-linkedpolyurethane/urea hybrid comprising the reaction product of water and anover-indexed thermoplastic polyurethane elastomer having an NCO index ofbetween about 1.01 and about 1.35, wherein the thermoplasticpolyurethane cross-linked polyurethane/urea hybrid is the reactionproduct of (a) a stoichiometric excess of at least about 1 mol percentof organic isocyanate moieties to the hydroxyl (or oxyhydrogen) moietiesof the other reactants in the reaction product: (b) an unsaturated diol,having two primary hydroxyl groups and at least one allyl ether sidegroup, of the formula

in which R¹ may be any substituted or unsubstituted alkyl, substitutedor unsubstituted aryl, substituted or unsubstituted alkyl-aryl group,substituted or unsubstituted ether group, substituted or unsubstitutedester group, any combination of the above groups, or H, and mayoptionally include an unsaturated bond in any main chain or side chainof any group; R² may be any suitable substituted or unsubstituted alkyl,substituted or unsubstituted aryl, substituted or unsubstitutedalkyl-aryl group, substituted or unsubstituted ether group, substitutedor unsubstituted ester group, any combination of the above groups; andR² includes an allyl group; and x and y are integers independentlyhaving any value from 1 to 10; (c) a chain extender, having at least tworeaction sites with isocyanates and having a molecular weight of lessthan about 450; (d) a long chain polyol having a molecular weight ofbetween about 500 and about 4,000 to form the precursor; (e) asufficient amount of free radical initiator, so as to be capable ofgenerating free radicals that induce cross-linking structures in thehard segments by free radical initiation to form a reaction product; and(f) water.
 18. The golf ball according to claim 17, wherein the NCOindex is between about 1.06 and 1.35.
 19. The golf ball according toclaim 17, wherein the at least 1 golf ball layer comprises a core and anouter core layer.
 20. The golf ball according to claim 17, wherein theat least 1 golf ball layer comprises a core and an inner cover layer.